One of my favorite passages reads as following
“In hope he believed against hope, that he should become the father of many nations, as he had been told, “So shall your offspring be.” He did not weaken in faith when he considered his own body, which was as good as dead (since he was about a hundred years old), or when he considered the barrenness of Sarah’s womb. No unbelief made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, fully convinced that God was able to do what he had promised.”
Abraham had faith that God did not lie
As already mentioned Abraham considered that God would bring Isaac back from the ashes
“By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only son, of whom it was said, “Through Isaac shall your offspring be named.” He considered that God was able even to raise him from the dead, from which, figuratively speaking, he did receive him back.”
Abraham wasn’t concerned about the how God will fulfill His end of the covenant, Abraham was concerned about obeying God which was his end of the covenant. He trusted God on his end and left all the other details to Him.